在c++中通过引用传递对象

Passing an object by reference in C++

本文关键字：对象 引用 c++      更新时间：2023-10-16

在人们开始让我用谷歌搜索我的问题之前，让我说一下，我已经尝试了很长时间了。

我不知道如何在c++中通过引用传递对象，我一直得到大量编译器错误的打印输出。如果他们有帮助，我可以把他们包括在内。具体来说，我试图通过引用线程中的函数parseFeed来传递RSSFeed对象feed。

void parseFeed(RSSFeed& feed) {
    //dostuff
}
RSSFeed feed();
thread(parseFeed, feed); // line 119

错误:

g++ -g -Wall -pedantic -O0 -std=c++0x -D_GLIBCXX_USE_NANOSLEEP -D_GLIBCXX_USE_SCHED_YIELD -I/usr/class/cs110/include/libxml2 -I/usr/class/cs110/local/include   -c -o news-aggregator.o news-aggregator.cc
In file included from /usr/include/c++/4.6/functional:56:0,
                 from /usr/include/c++/4.6/bits/stl_algo.h:68,
                 from /usr/include/c++/4.6/algorithm:63,
                 from news-aggregator.cc:14:
rss-feed.h: In constructor âconstexpr std::_Head_base<_Idx, _Head, false>::_Head_base(const _Head&) [with long unsigned int _Idx = 0ul, _Head = RSSFeed]â:
/usr/include/c++/4.6/tuple:162:44:   instantiated from âconstexpr std::_Tuple_impl<_Idx, _Head, _Tail ...>::_Tuple_impl(const _Head&, const _Tail& ...) [with long unsigned int _Idx = 0ul, _Head = RSSFeed, _Tail = {}]â
/usr/include/c++/4.6/tuple:423:24:   instantiated from âconstexpr std::tuple<_T1>::tuple(const _T1&) [with _T1 = RSSFeed]â
/usr/include/c++/4.6/functional:1362:70:   instantiated from âstd::_Bind_result<_Result, _Functor(_Bound_args ...)>::_Bind_result(_Functor&&, _Args&& ...) [with _Args = {RSSFeed&}, _Result = void, _Functor = void (*)(RSSFeed&), _Bound_args = {RSSFeed}]â
/usr/include/c++/4.6/functional:1477:41:   instantiated from âtypename std::_Bindres_helper<_Result, _Functor, _ArgTypes>::type std::bind(_Functor&&, _ArgTypes&& ...) [with _Result = void, _Functor = void (&)(RSSFeed&), _ArgTypes = {RSSFeed&}, typename std::_Bindres_helper<_Result, _Functor, _ArgTypes>::type = std::_Bind_result<void, void (*(RSSFeed))(RSSFeed&)>]â
/usr/include/c++/4.6/thread:135:9:   instantiated from âstd::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (&)(RSSFeed&), _Args = {RSSFeed&}]â
news-aggregator.cc:119:25:   instantiated from here
rss-feed.h:54:3: error: âRSSFeed::RSSFeed(const RSSFeed&)â is private
/usr/include/c++/4.6/tuple:97:25: error: within this context
/usr/include/c++/4.6/tuple:97:25: error: use of deleted function âRSSFeed::RSSFeed(const RSSFeed&)â
rss-feed.h:54:3: error: declared here
rss-feed.h: In constructor âstd::_Head_base<_Idx, _Head, false>::_Head_base(_UHead&&) [with _UHead = RSSFeed, long unsigned int _Idx = 0ul, _Head = RSSFeed]â:
/usr/include/c++/4.6/tuple:174:43:   instantiated from âstd::_Tuple_impl<_Idx, _Head, _Tail ...>::_Tuple_impl(std::_Tuple_impl<_Idx, _Head, _Tail ...>&&) [with long unsigned int _Idx = 0ul, _Head = RSSFeed, _Tail = {}, std::_Tuple_impl<_Idx, _Head, _Tail ...> = std::_Tuple_impl<0ul, RSSFeed>]â
/usr/include/c++/4.6/tuple:434:51:   instantiated from âstd::tuple<_T1>::tuple(std::tuple<_T1>&&) [with _T1 = RSSFeed, std::tuple<_T1> = std::tuple<RSSFeed>]â
/usr/include/c++/4.6/functional:1368:78:   instantiated from âstd::_Bind_result<_Result, _Functor(_Bound_args ...)>::_Bind_result(std::_Bind_result<_Result, _Functor(_Bound_args ...)>&&) [with _Result = void, _Functor = void (*)(RSSFeed&), _Bound_args = {RSSFeed}, std::_Bind_result<_Result, _Functor(_Bound_args ...)> = std::_Bind_result<void, void (*(RSSFeed))(RSSFeed&)>]â
/usr/include/c++/4.6/functional:1477:41:   instantiated from âtypename std::_Bindres_helper<_Result, _Functor, _ArgTypes>::type std::bind(_Functor&&, _ArgTypes&& ...) [with _Result = void, _Functor = void (&)(RSSFeed&), _ArgTypes = {RSSFeed&}, typename std::_Bindres_helper<_Result, _Functor, _ArgTypes>::type = std::_Bind_result<void, void (*(RSSFeed))(RSSFeed&)>]â
/usr/include/c++/4.6/thread:135:9:   instantiated from âstd::thread::thread(_Callable&&, _Args&& ...) [with _Callable = void (&)(RSSFeed&), _Args = {RSSFeed&}]â
news-aggregator.cc:119:25:   instantiated from here
rss-feed.h:54:3: error: âRSSFeed::RSSFeed(const RSSFeed&)â is private
/usr/include/c++/4.6/tuple:101:42: error: within this context
/usr/include/c++/4.6/tuple:101:42: error: use of deleted function âRSSFeed::RSSFeed(const RSSFeed&)â
rss-feed.h:54:3: error: declared here

:线程(parseFeed, ref (饲料) );//第119行

This 

RSSFeed feed();

是一个函数声明，它返回一个RSSFeed类型的对象，没有参数。它不是一个对象定义。

写而不是

RSSFeed feed;

另外，从错误消息列表中可以看出，类RSSFeed没有复制构造函数，也就是说它被定义为已删除。

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